This invention relates to a method of consolidating poor quality soils, and in particular to a method of consolidating soils in which a poor quality solid or a water leaking soil is modified into a uniformly and strongly consolidated soil or a water-tight soil.
In this specification, the term "a poor quality soil or a loose soil" is intended to designate a loose or water leaking soil encountered in building foundation excavation work or in subway (or underground railway) excavation work. The term "consolidation of a poor quality soil" is intended to mean that various hardners are injected into a poor quality soil to consolidate the latter, thereby to provide a strong and water-proof soil or a water-tight soil.
In general, such a poor quality soil is formed by a coarse soil layer (including air gaps) and a fine soil layer mutually overlapped or laid one on another. Accordingly, it is necessary to consolidate the poor quality soil by injecting hardeners thereinto.
In this invention, the uniform consolidation of a poor quality soil means that both of the coarse soil layer and the fine soil layer mentioned above are consolidated thereby to improve not only the strength but also the water-tight characteristic of the soil. The consolidation of only one of the two layers forming the soil cannot be regarded as the uniform consolidation of the soil intended by this invention, and cannot increase the strength of the soil nor provide a water-tight soil.
The following method of consolidating a poor quality soil is well known in the art:
1. Dual-Liquid Water Glass Method
In this conventional method, an aqueous solution of inorganic gelling agent or a suspension containing cement (liquid-A) and a water glass aqueous solution (liquid-B) are employed as hardeners. These hardeners, or the liquid A or the liquid B, are joined together by a Y-shaped pipe, and the resultant liquid (hereinafter referred to as an liquid-AB) is injected into a soil to be consolidated. This method is simple in operation and superior in consolidation; however, it suffers from the following disadvantages.
A. The liquid-A and the liquid-B are hardenders which will cause reaction by blending and consolidate. However, if they are left as unreacted materials in a soil, it will cause a problem such as water pollution. Especially, if the liquid-B is left as an unreacted material in a soil, it leaks into the subterranean water in the soil thus causing a serious public hazard. Accordingly, in order to overcome this difficulty, or in order not to leave such an unreacted material in the soil, it is necessary to join the liquid-A and the liquid-B together at a certain ratio thereof.
However, to do so practically is extremely difficult. Especially, in the case where the injection pressures of the liquids are high or the injection quantities of the liquids are little, the injection ratio of the liquid-A to the liquid-B greatly fluctuates, and at worst only one of the two liquids is injected. Accordingly, in this conventional method, the unreacted material is liable to be left in the soil, which leads to the occurrence of a public hazard such as water pollution.
B. Upon blending, the liquid-A and the liquid-B are quickly gelatinized. In the case where the liquid-A contains cement, the liquid obtained by joining the liquid-A and the liquid-B becomes a suspension since the liquid-A containing the cement is also a suspension. Accordingly, the liquid-AB is poor in permeability and therefore cannot permeate further than a coarse soil layer.
Thus, in this method, a fine soil layer is scarcely permeated by the hardeners, as a result of which the soil treated by this method is undoubtedly ununiform in quality.
2. Water Glass Injection Method Utilizing Organic Gelling Agent
This conventional method is a solution type water glass utilizing aldehyde compound or ester as a gelling agent, and its gelation time can be made considerably long. Accordingly, in this method, the liquid-joining step as described above in unnecessary, and further, the water glass and the gelling agent are accurately compounded in advance and injected by a so-called one shot method. Furthermore, since it is a solution type-chemical liquid, it can be uniformly injected into a fine soil layer. However, this conventional method also has a difficulty. That is, since the gelling agent is an aqueous solution, the hardener has an excellent permeability. Owing to this characteristic, the hardener is liable to leak from the air gaps or the coarse soil layer into a part of the soil other than injected. Therefore, it is difficult to consolidate great air gaps and a coarse soil layer in a soil to be consolidated. Accordingly, it is also difficult to form or obtain a uniformly consolidated soil by this conventional method.